343 Guilty Spark
The personality of 343 Guilty Spark is somewhat eccentric and egotistical to the point of solipsism. The long period of isolation experienced by it may have contributed, or even been the cause, of much of this. 343 Guilty Spark is in a state of Rampancy; although he is still accepting of his role as Monitor, his pursuit of alien knowledge does seem to go beyond his purpose. Since it was his job to manage the Flood, he was also trained to learn. It was intended for him to learn so he could stand ready for any changes in the Flood. However this system is his greatest weakness and he applies it to everything. He loves to learn and to take records; even if he has to force it out. While solipsistic much of the time, he seems to be aware of the limitations of his knowledge, such as when he perceived Installation 00 to be part of a Shield Installation, and not what it was all along.
Ur-Didact
Shadow-of-Sundered-Star, more commonly known as the Ur-Didact (Ur-meaning original), was a Forerunner Promethean who held an extremely high status in the Forerunner society as supreme commander of the entire Forerunner military. He wholeheartedly believed in the Mantle of Responsibility the Forerunners held to protect life, and initially opposed theHalo Array as a sin beyond measure. He was also the lover and husband ofThe Librarian.
The Librarian
First-Light-Weaves-Living-Song, more commonly known as The Librarian, was a Forerunner who served as the Lifeshaper (leader of the Lifeworker caste). She sought to document and index all sentient beings of the Milky Way and protect them from being absorbed into the Flood by sending them to the shelter of the Ark. Of all the races she indexed, she deeply respected Humanity, whom she viewed as "special" among all of the sentient life she had seen: she felt that saving them was well-worth dying for.